The subject invention is related to improvements in gaseous ion lasers. It is particularly suited for use in a conduction cooled ion laser of the type disclosed in U.S. Pat. Nos. 4,378,600 issued Mar. 29, 1983 to Hobart and 4,376,328 issued Mar. 15, 1983 to Mefferd, both assigned to the same assignee as the subject invention and incorporated herein by reference.
The type of gaseous ion laser disclosed in the latter patents includes a relatively thin-walled, electrically insulating outer envelope, formed from a ceramic material, such as an alumina tube. A plurality of thin-walled heat conducting members are mounted in spaced-apart relation along the length of the envelope or tube and placed in thermal contact therewith. In the latter patents, the heat conducting members are permanently affixed to the inner wall of the tube. Each of the heat conducting members in the above cited patents include a central aperture surrounded by a sputter-resistant material, for extending the life of the tube. All the apertures are aligned in assembly to define a straight discharge path. The tube is also provided with electrodes for exciting the gas within the tube and an optical cavity aligned along the discharge path.
In one aspect of the invention disclosed in the Hobart patent, gas pressure imbalances can be controlled through the use of cylindrical ring gas barriers, coaxially mounted within the tube, to separate the central discharge from an internal gas return path. In the latter patent, the internal gas return path is defined by a plurality of apertures formed in the outer periphery of the heat conducting members. It had been found that without the cylindrical ring gas barriers, the internal gas return path was insufficient to prevent the pressure differential built up by gas pumping in the discharge from significantly lowering output power of the laser or extinguishing the discharge. In such a case, it may be necessary to provide an external gas bypass, such as a tube outside of the insulating envelope and connected between the anode and cathode of the laser, to reduce this pressure differential. With the addition of the cylindrical ring gas barrier, an internal bypass alone is sufficient to compensate for gas pumping and an external gas bypass can be eliminated.
The device disclosed in the Hobart and Mefferd patents has been successfully manufactured for a considerable time. Argon ion lasers having a discharge tube approximately two feet in length are capable of generating 5 watts of continuous output power in the visible spectrum over the warranted lifetime of the product. An output in the ultraviolet spectrum on the order of 200 milliwatts can also be generated. These outputs are achieved when the laser is operated at 40 amperes of current.
As can be appreciated, it is always desirable to produce higher output powers for a given envelope size. It is known that more output power can be produced if the operating current is increased, or the pressure is decreased. Unfortunately, the discharge in the tube tends to become unstable when either the current is increased or the pressure is decreased beyond set levels. By instability it is meant that ionization waves in the discharge grow to large amplitudes (i.e., there are radio-frequency current oscillations on top of the direct current discharge), which if left unchecked, can lead to catastrophic results. These high-frequency current oscillations need not terminate on the normal electrodes, but can extend into parts of the tube that are not directly cooled, and thus possibly crack the ceramic envelope or damage other laser components.
Accordingly, it is an object of the subject invention to provide a new and improved gaseous ion laser which includes an improved gas barrier configuration for enhancing power output.
It is another object of the subject invention to provide a new and improved gaseous ion laser which uses a reentrant gas barrier design for enhanced operation.
It is a further object of the subject invention to provide a reentrant shield configuration which is easy to accurately manufacture and enhances the separation between hot, on-axis ions and the cool return flow of atoms.